This invention relates to a composite material having diamonds bonded into an amorphous metal matrix.
Hard, abrasive materials such as certain carbides, borides, and nitrides are widely used to cut other, softer materials such as metals. Large single pieces of these hard, abrasive materials are too brittle and too expensive for many cutting-tool applications. A bonded-tool technology has developed over the years for using smaller pieces of such materials in cutting tools. In this approach, small particles of the hard, abrasive material are bonded at elevated temperatures into a matrix of a metal such as a nickel or cobalt alloy by liquid phase sintering. This process requires considerable exposure time of the components at elevated temperatures. Upon cooling, the resulting composite material has the particles of the hard, abrasive material dispersed throughout the metal matrix. The metal matrix bonds the particles together and also imparts fracture toughness and thermal conductivity to the article. As one example of this type of material, tungsten carbide/cobalt alloy cutting tools are widely used commercially.
When such a composite material is used as a cutting tool, the surface regions of the metal matrix quickly wear away to expose the pieces of the hard, abrasive material. This exposed region acts as the cutting instrument, inasmuch as it is hard, abrasive, durable, and unlikely to wear away during the cutting operation. However, the underlying metal matrix which bonds the hard, abrasive material can wear away or crack with extended use.
Diamond is the hardest known substance, and is therefore desirably used in cutting tools. Diamond/metal-matrix composite cutting tools: have been made. However, in most cases these cutting tools are expensive because relatively expensive, high-purity natural diamond is used. Lower grade natural or artificial diamond tends to chemically degrade by graphitization in the high-temperature sintering process by which the diamond particles are bonded to the metal matrix. Additionally, in many instances the diamond/metal-matrix composite materials have yielded less than the expected cutting performance because the metal matrix is not sufficiently resistant to abrasion and fracture. Consequently, the metal matrix wears away and/or fractures relatively quickly, resulting in the loss of the cutting edge.
There is a need for an improved approach by which low-grade artificial or natural diamonds can be used in cutting implements. The present invention fulfills this need, and further provides related advantages.